1. Field of the Invention
The present invention relates to microfluidic devices, and more particularly to techniques for reducing the number of input and output connections required to connect a microfluidic device to an external controller for controlling the microfluidic device.
2. Description of the Related Art
Micro/nano technology devices are known in the art as devices with components on the scale of 1 μn to 100s of μm that cooperate to perform various desired functions. In particular, microfluidic devices are micro/nano technology devices that perform fluid handling functions which, for example, cooperate to carry out a chemical or biochemical reaction or analysis.
Microfluidic devices include a variety of components for manipulating and analyzing the fluid within the devices. Typically, these elements are microfabricated from substrates made of silicon, glass, ceramic, plastic, and/or quartz. These various fluid-processing components are linked by microchannels, etched into the same substrate, through which the fluid flows under the control of a fluid propulsion mechanism. Electronic components may also be fabricated on the substrate, allowing sensors and controlling circuitry to be incorporated in the same device. Because all of the components are made using conventional photolithographic techniques, multi-component devices can be readily assembled into complex, integrated systems.
Most microfluidic devices in the prior art are based on fluid flowing through micro-scale passages and chambers, either continuously or in relatively large aliquots. Fluid flow is usually initiated and controlled by electro-osmotic and electrophoretic forces. See, e.g., U.S. Pat. No. 5,632,876, issued Apr. 27, 1997 and entitled “Apparatus and Methods for Controlling Fluid Flow in Microchannels;” U.S. Pat. No. 5,992,820, issued Nov. 30, 1999 and entitled “Flow Control in Microfluidics Devices by Controlled Bubble Formation;” U.S. Pat. No. 5,637,469, issued Jun. 10, 1997 and entitled “Methods and Apparatus for the Detection of an Analyte Utilizing Mesoscale Flow Systems;” U.S. Pat. No. 5,800,690, issued Sep. 1, 1998 and entitled “Variable Control of Electroosmotic and/or Electrophoretic Forces Within a Fluid-Containing Structure Via Electrical Forces;” and U.S. Pat. No. 6,001,231, issued Dec. 14, 1999 and entitled “Methods and Systems for Monitoring and Controlling Fluid Flow Rates in Microfluidic Systems.” See also products from, e.g., Orchid, Inc. (www.orchid.com) and Caliper Technologies, Inc. (www.calipertech.com).
Microfluidic devices that manipulate very small aliquots of fluids (know herein as “micro-droplets”) in micro-scale passages rely principally on pressure and other non-electric forces to move the liquid volume. These devices are advantageous because smaller volumes of reagents are required and because non-electric propulsion forces can be generated using relatively small voltages, on the same order of magnitude as voltages required by standard microelectronic components. See, i.e. the following patents, the contents of which are incorporated herein in their entirety by reference: U.S. Pat. No. 6,057,149, issued May 2, 2000 and entitled “Microscale Devices And Reactions In Microscale Devices;” U.S. Pat. No. 6,048,734, issued Apr. 11, 2000 and entitled “Thermal Microvalves in a Fluid Flow Method;” and U.S. Pat. No. 6,130,098, issued Oct. 10, 2000. (Citation or identification of any reference in this section or any section of this application shall not be construed that such reference is available as prior art to the present invention).
U.S. Pat. No. 6,130,098 (“the '098 patent”), for example, discloses microfluidic devices that include micro-droplet channels for transporting fluid droplets through a fluid processing system. The system includes a variety of micro-scale components for processing the fluid droplets, including micro-reaction chambers, electrophoresis modules, and detectors (such as radiation detectors). In some embodiments, the devices also include air chambers coupled to resistive heaters to internally generate air pressure to automatically withdraw a measured volume of fluid from an input port, and to propel the measured micro-droplet through the microfluidic device.
These components are connected to input/output (I/O) pins at the edge of the micro-fluid device which mate with corresponding I/O pins of the external controller. The external controller operates these components by sending and receiving control signals via the input/output pins. For example, a control device, external to the microfluidic device, activates a resistive heater within a microfluidic device by supplying current to the heater through the input/output pins. Microfluidic devices can include a large number of such components which are controlled by external devices. Accordingly, an object of the present invention is to reduce the number of input/output pins required for controlling such microfluidic devices from such external controllers.